Self-Assembled Monolayer Exchange Reactions as a Tool for Channel Interface Engineering in Low-Voltage Organic Thin-Film Transistors

Abstract

In this work, we compared the kinetics of monolayer self-assembly long-chained carboxylic acids and phosphonic acids on thin aluminum oxide surfaces and investigated their dielectric properties in capacitors and low-voltage organic thin-film transistors. Phosphonic acid anchor groups tend to substitute carboxylic acid molecules on aluminum oxide surfaces and thus allow the formation of mixed or fully exchanged monolayers. With different alkyl chain substituents (n-alkyl or fluorinated alkyl chains), the exchange reaction can be monitored as a function of time by static contact angle measurements. The threshold voltage in α,α'-dihexyl-sexithiophene thin-film transistors composed of such mixed layer dielectrics correlates with the exchange progress and can be tuned from negative to positive values or vice versa depending on the dipole moment of the alkyl chain substituents. The change in the dipole moment with increasing exchange time also shifts the capacitance of these devices. The rate constants for exchange reactions determined by the time-dependent shift of static contact angle, threshold voltage, and capacitance exhibit virtually the same value thus proving the exchange kinetics to be highly controllable. In general, the exchange approach is a powerful tool in interface engineering, displaying a great potential for tailoring of device characteristics.

Quantitative Determination and Comparison of the Surface Binding of Phosphonic Acid, Carboxylic Acid, and Catechol Ligands on TiO2 Nanoparticles

“…To this end, the increasing binding strength in the order CA<Cat<PA was first confirmed in desorption experiments. Static contact angle (SCA) experiments are a good measure of the stability of self‐assembled monolayers on flat substrates . To this end, thin flat 2D TiO 2 layers were functionalized with phosphonic acid, carboxylic acid, and catechol molecules.…”

“…Ligand exchange reactions are a fundamental concept in the field of surface modification of metal oxides . Moreover, many wet‐synthetic procedures of nanoparticles involve organic adlayers attached to the particle surface, mainly for maintaining colloidal stability.…”

Structural Investigations of Self-Assembled Monolayers for Organic Electronics: Results from X-ray Reflectivity

“…A monolayer of 12,12,13,13,14,14,15,15,16,16,17,17,18,18,18H-pentadecafluoro-octadecyl phosphonic acid (F 15 C 18 -PA, Figure 1a) with 15 fluorine atoms (C 18 -PA with partially substituted hydrogen atoms) was investigated. The molecule has a similar theoretical length as C 18 -PA but with a presumably higher electron density due to the electron rich fluorine.…”

Nanopatterning on H-Terminated Si(111) Explained as Dynamic Equilibrium of the Chemical Reaction with Methanol

“…These rates are recalculated at each cycle according to the state of lattice at the beginning of the cycle. Reaction rates k were calculated using DFT barrier values E (found in Table 1) in the transition state theory (TST) expression (4) where P events is the desired event density (typically 0.001) and N sites is the number of sites in the simulated lattice. The simulated time duration of each cycle is…”